Hello to all! First of all great forum, it's my first post 
I've just bought a cmoy amp from ebay, here is the link -> http://cgi.ebay.it/ws/eBayISAPI.dll?ViewItem&ih=012&viewitem=&item=220087565178&rd=1&rd=1
It seems to work, but from middle to high volume the sound, especially the low frequences, distorts. I don't like this because the output signal from my audio card without the amp is higher (and cleaner) than with that...
Can I make some changes to solve this problem?
Here are some photos of the cmoy
http://img137.imageshack.us/img137/3869/img00211mm8.jpg
http://img154.imageshack.us/img154/136/img00205cr4.jpg
Thanks, and sorry for my bad english
I've just bought a cmoy amp from ebay, here is the link -> http://cgi.ebay.it/ws/eBayISAPI.dll?ViewItem&ih=012&viewitem=&item=220087565178&rd=1&rd=1
It seems to work, but from middle to high volume the sound, especially the low frequences, distorts. I don't like this because the output signal from my audio card without the amp is higher (and cleaner) than with that...
Can I make some changes to solve this problem?
Here are some photos of the cmoy
http://img137.imageshack.us/img137/3869/img00211mm8.jpg
http://img154.imageshack.us/img154/136/img00205cr4.jpg
Thanks, and sorry for my bad english
Looks like a quality board. What is the impedance of your headphones? My guess is that it just lacks enough current to drive them.
The opamp is in a socket so it would be easy to try something like OPA2134 to see if it makes any difference, but I doubt it will. If you want more current capability without making any modifications you could try two OPA551 single opamps in a dual adapter.
The opamp is in a socket so it would be easy to try something like OPA2134 to see if it makes any difference, but I doubt it will. If you want more current capability without making any modifications you could try two OPA551 single opamps in a dual adapter.
If it works otherwise, I would try adding a large value capacitor between the wires from the battery, assuming it runs off 9V you should be able to get a big value 2200uf and more, small size, low voltage one from say, a dead/obsolete PC motherboard...
Looks like a nice opa2228 circuit that, would love to see a schematic, but I guess thats not possible.
Those chips are quite hard to stabalise and are also set up slightly diffirent from other opamps in terms of resitor to ground on input side... so your mileage with other opamps will vary... not saying it won't work.
In my experience opa2228 is one of the best opamps I have heard...provided it is stable...
BTW it is not a cmoy that... anything but. If it works it should be much better.
Let us hear about your progress...
Looks like a nice opa2228 circuit that, would love to see a schematic, but I guess thats not possible.
Those chips are quite hard to stabalise and are also set up slightly diffirent from other opamps in terms of resitor to ground on input side... so your mileage with other opamps will vary... not saying it won't work.
In my experience opa2228 is one of the best opamps I have heard...provided it is stable...
BTW it is not a cmoy that... anything but. If it works it should be much better.
Let us hear about your progress...
Nordic,
I can see from the picture he posted that it is clearly the basic "cmoy" circuit with rail splitter. I can see the 100k input resistor to ground, the gain resistors of 1k/6.04k, and the output resistor of 75R.
I know the headphone amp in the data sheet for the OPA2228 is quite a bit different than the cmoy, but it obviously works with this configuration as well. Maybe that is the problem, I don't know.
There really isn't much you can do to fix the problem PxPert. I suggest you measure the impedance of your headphones so you can get a better idea of what is going on.
If you want, I can mail you an OPA2134 for you to experiment with, though I doubt it will help.
I can see from the picture he posted that it is clearly the basic "cmoy" circuit with rail splitter. I can see the 100k input resistor to ground, the gain resistors of 1k/6.04k, and the output resistor of 75R.
I know the headphone amp in the data sheet for the OPA2228 is quite a bit different than the cmoy, but it obviously works with this configuration as well. Maybe that is the problem, I don't know.
There really isn't much you can do to fix the problem PxPert. I suggest you measure the impedance of your headphones so you can get a better idea of what is going on.
If you want, I can mail you an OPA2134 for you to experiment with, though I doubt it will help.
I've tried to add a 1000uf 25v capacitor but with no luck...
So there are no solutions... And if i make an amplifier OPA2228 based from scratch?
Where can I get a simple (and efficent) scheme to build it?
I think with a simple scheme i could make it without problems
Anyway, I've unsoldered most of the upper components and made a photo of the upper and lower side of the circuit, I hope you can make a scheme for this circuit from the photos if you are interested. When I'll come back home I'll post them.
Thanks to theAnonymous & Nordik!
So there are no solutions... And if i make an amplifier OPA2228 based from scratch?
Where can I get a simple (and efficent) scheme to build it?
I think with a simple scheme i could make it without problems
Anyway, I've unsoldered most of the upper components and made a photo of the upper and lower side of the circuit, I hope you can make a scheme for this circuit from the photos if you are interested. When I'll come back home I'll post them.
Thanks to theAnonymous & Nordik!
If you can figure out which is the feedback resistor, (will go from output to input) try to parallel it with a small cap in the 2 - 12pf range, this should counter any instability...
In my experience that chip does not sound its best in the default cmoy circuit, so a new chip aught to fix the problem... look at ne5532 and opa2312 or opa2134, if you can't find any we can arrange one for you.
In my experience that chip does not sound its best in the default cmoy circuit, so a new chip aught to fix the problem... look at ne5532 and opa2312 or opa2134, if you can't find any we can arrange one for you.
please let us know .....
Ok, first I'm new at this but when I saw the pic of the board (which looked very good) the first thing I thought was they put the 2228 in a circuit designed around a 2134. I'm very interested in what you find as I just finished a CMoy and I'd like to try other chips. If you post your impressions it might narrow the number of chips I'd want to buy and the circuit tweeks I'd have to make.
Ok, first I'm new at this but when I saw the pic of the board (which looked very good) the first thing I thought was they put the 2228 in a circuit designed around a 2134. I'm very interested in what you find as I just finished a CMoy and I'd like to try other chips. If you post your impressions it might narrow the number of chips I'd want to buy and the circuit tweeks I'd have to make.
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